A typical brush motor comprises a stator and a rotor which comprises a rotor core having a number of salient rotor poles separated by slots, a commutator and windings wound about the poles of the rotor core. An insulator may be disposed within each slot for insulating the rotor core from the windings. A traditional brush wave winding motor usually adopts the same number of rotor slots (rotor poles) and commutator segments, for example 25 rotor slots and 25 commutator segments.
It is usual to describe the construction of a motor by the number of stator poles, rotor poles and commutator segments. As the number of rotor poles is equal to the number of slots defined by the rotor poles, it is conventional to refer to the number of rotor poles as the number of slots to avoid confusion with the stator poles. It is also conventional to refer to commutator segments as bars, e.g. a 4 pole 25 slot 25 bar motor refers to a motor with 4 stator poles, 25 rotor poles and 25 commutator segments. If the number of commutator segments is equal to the number of rotor poles, as is the usual case, they are not mentioned thus the motor of the above example would simply be referred to as a 4 pole 25 slot motor.
However, the slot fill factor (the ratio of the total cross sectional area of the insulated wires within the slot and the cross sectional area of the slot) of this kind of traditional brush wave winding motor is relatively low, especially when a small motor has a large number of narrow rotor slots, which limits the performance of the motor.
Hence there is a desire for an improved brush motor with a high slot fill factor.